Product



June 27, 1961 R. E. EDWARDS, JR., ET AL METHOD OF RECOVERING HIGH-PURITY NAPHTHALENE Filed Aug. 5, 1959 F g l SOD/UM i sroma: I MIX" /29 28 l I52 I j l .igj a'l l l I l 30 'PRODUCT NITROGEN L 7 23 I3 22 HOLD/N61. 48 I TANK CONDENSER DELANTER /7 FRAcrm/vA TING i comps/v.95}? STIILL CONTAMINATED NDENSER REACTOR VESSEL 6 l0 DEl-IYDRA TOR I-IEA r51? STEAM H nus/1c rA NK 0/L Z5 4 27- CONTAMINATED WA rm //V VE/V T 0R5 R/CHARD E EDWARDS, a, JAMES L. PFLASTERER and RONA L D M.

United States Patent 2,990,435 METHOD OF RE'COVERING HIGH-PURITY NAPHTHALENE Richard E. Edwards, Jr., Whitehall, James L. Pilasterer,

'Greentree, and Ronald M. Smeaton, Bethe], Pa., assignors to United States Steel Corporation, a corporation of New Jersey Filed Aug. 5, 1959, 'Ser. No. 831,810 1 Claim. (Cl. 260-674) This invention relates to the production of naphthalene and, in particular, a high-purity product with a very low sulphur content.

Naphthalene is ordinarily recovered by cystallizattion on cooling a relatively broad fraction of carbolic oil distilled from coal tar. This is a slow, expensive method involving high equipment maintenance and the product is not of a high standard of purity, especially in respect to sulphur content and crystallizing point, because of physical entrapment of the oil with the crystals and the similarity of the physical characteristics of the contaminants.

We have invented a novel method for recovering naphthalene which, speaking generally, involves the treatment with metallic sodium of a relatively narrow fraction of crude carbolic oil at a temperature above the melting point of sodium, followed by distillation of the reaction mixture. The product naphthalene taken overhead from the still has a crystallizing temperature of better than 79.5 C., and less than .05% sulphur. We are aware that treatment of relatively pure naphthalene with SOdlllfil has been resorted to for reducing the sulphur content. By our method, however, we are able to eliminate crystallization by purifying crude naphthalene feed with sodium and then separating the naphthalene from the sulphurized impurities which are physically dissimilar, by distillation. This avoids the difficultes inherent in the crystallization practice.

A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawing illustrating the present preferred embodiment. The single figure of the drawing is a diagrammatic showing of the apparatus used in carrying out our method.

The preferred practice of our invention will be explained in detail by reference to the system illustrated in the drawing. We preferably take from carbol-ic oil, by fractional distillation, the fraction boiling between 210 and 230 C., although a somewhat broader fraction, say that boiling between 200 and 250 C. may be treated with advantage by our method. We agitate with this fraction a dispersion of molten sodium in naphthalene, in an amount such that the sodium present is about 2% by weight of the naphthlene being treated. The agitation is continued for a substantial period such as 90 minutes and the mixture is maintained at elevated temperature, i.e., 2l0 C. or higher. After the described sodium treatment, the oil fraction is distilled and the product naphthalene taken overhead. The bottoms comprising residual sodium, sodium sulphide, some naphthalene and oil, may be disposed of or used as desired.

Referring more particularly to the drawing, we deliver the preferred carbolic-oil cut, after washing with dilute alkali, saturated with water, through a supply pipe to a dehydrator 11 at about 90 C. The entering stream is predominantly impure naphthalene with a crystallizing temperature of about 75 C. The dehydrator may be a vacuum evaporating chamber or a small still. Vapor from the dehydrator is cooled at 12 and condensed in a decanter 13. Water from the latter is wasted and the oil is returned to feed pipe 10. Dry naphthalene from de hydrator 11 is pumped through a heater 14 to a reactor vessel 15 provided with a heating coil 16 and a condenser 17.

From a holding tank 18, we discharge into vessel 15 a metered quantity of a dispersion of molten sodium in naphthalene. The relative proportions of sodium and naphthalene are not too important. The sodium may account for from 20 to 60% of the dispersion by weight, preferably about 50%. The amount of the dispersion delivered to vessel 15 should be such, in proportion to the crude naphthalene feed, that the sodium present will be about 2% by weight of the naphthalene being treated although an excess of sodium will not impair the reaction. The mixture is agitated while it is held in vessel 15 by an impeller 19 driven at about 2500 rpm, for about minutes, and heat is preferably applied by coil 16 to keep the temperature of the mixture at about 210 C.

After the desired reaction time, the mixture is pumped, while still at the temperature stated, through a heater 20 to a fractionating still 21 provided with a condenser 22. As a result of the heat added by heater 20, the mixture boils in the still and naphthalene vapor flows through condenser 22 and product pipe 23 to storage or a shipping point. The bottoms are quenched by steam in tank 24, thus killing any residual metallic sodium, and then sent through a decanter 25. Oil from the latter flows from pipe 26 to be reclaimed. Water flows from pipe 27 to waste.

Sodium for making the naphthalene-sodium treating mixture is kept in a storage hopper 28. The mixture is formed in a mixer 29 fed by metering devices 29a and 29b. Mixer 29 has an agitator 30 and a heat-exchange coil 31. Naphthalene is supplied to the mixer by a pipe 32 tapped into delivery line 23. The mixture of sodium and naphthalene should be kept at a temperature not higher than C. during agitation in mixer 29, to prevent adverse reaction of sodium and naphthalene. Nitrogen or other inert gas is supplied to the mixer and to tanks 18 and 28 through pipes 33.

Naphthalene taken off through pipe 23 has a crystalling temperature of better than 79.5 C. and a sulphur content not higher than .05%. It is thus higher in quality than naphthalene recovered by crystallization on cooling carbolic oil, followed by distillation.

Instead of using the fractionating still 21, a small vacuum flash chamber maybe substituted. The purity of the product will not be as high, however, as that of the naphthalene recovered by fractional distillation.

In addition to improved quality of product, our invention provides a simple and efficient method, characterized by better yield and lower operating cost than are possible with the crystallization process followed by distillation.

Although we have disclosed herein the preferred practice of our invention, we intend to cover as well any change or modification therein which may be made with out departing from the spirit and scope of the invention.

We claim:

A method of recovering naphthalene from carbolic oil which consists in distilling the oil and washing the fraction boiling between about 2.10 and 230 F. with a dilute water solution of distil the mixture of oil and solution to remove the water, agitating the remaining oil fraction with metallic sodium while maintaining the oil fraction at a temperature above the melting point of sodium, and then pumping the fraction to a. fractionating tower whereby relatively pure naphthalene vapor is evolved therefrom.

References Cited in the file ofthis patent Y UNITED STATES PATENTS 

